Microcalorimetric investigations of the host-parasite relationship between Biomphalaria glabrata and Schistosoma mansoni (author's transl)

1. The ratio of dry weight to wet weight of infected snails (5.5 +/- 2.2%) is significantly smaller than that of uninfected animals (8.3 +/- 1.0%). 2. The specific values of oxygen consumption and heat-production per dry weight are significantly higher for infected snails (2.41 +/- 0.44 microliter O2/h/mg; 12.63 +/- 1.24 muW/mg) than for uninfected ones (1.88 +/- 0.24 microliter O2/h/mg, 8.94 +/- 0.91 muW/mg). 3. The rate of oxygen consumption always suffices to explain the measured heat flows for aerobic catabolism of carbohydrates or fats and proteins, respectively. Neither for infected nor for uninfected snails is it necessary to assume an anaerobic energy metabolism. 4. Structures in the calorimetrically obtained heat production curves are discussed.     

Respiratory concerts revealed by scanning microrespirography in a termite Prorhinotermes simplex (Isoptera: Rhinotermitidae)

Respiratory metabolism of different developmental stages (larvae, pseudergates, nymphs, soldiers, neotenic reproductives; 0.6-4.5 mg body mass) of Prorhinotermes simplex was individually monitored by scanning respirographic method sensitive to subnanoliter amounts of O(2) consumption or CO(2) output per minute. Specimens exposed to dry air after removal from the colony performed enormously large, discontinuous bursts of CO(2) lasting usually 2 min. The volume of CO(2) produced during the burst often surpassed the volume of the whole body and it was 10- to 20-fold in excess of the air-filled endogenous tracheal volume. The initial velocity of CO(2) production during the burst was more than 90-fold faster in comparison to O(2) consumption. In the presence of enough moisture within the respiratory vessel, the termites breathed continuously without any larger outburst of CO(2). This fact fully corroborates validity of the so-called water retention theory in discontinuous CO(2) release. The highest rates of O(2) consumption were found in the second instar larvae (0.9 mg, 1000-2000 microl O(2)/g/h), the soldier caste was intermediate (700 microl O(2)/g/h) while pseudergates and neotenic reproductives consumed between 300 and 600 microl O(2)/g/h, at 25 degrees C. All developmental stages feeding on a cellulose diet had CO(2)/O(2) values (RQ) over 1 (1.2-1.4, i.e. carbohydrate metabolism), pigmented soldiers fed by the workers had RQ around 0.75 (predominating lipid or protein metabolism). The unusually large, sudden eruptions of CO(2) in specimens exposed to dry air allow us to make the following conclusions: (1) the bursts were due to special chemical processes, such as by enzymatic hydration of carbonic acid by carbonic anhydrase and; (2) the bulk of chemically evolved gaseous CO(2) escaped from the body by a mass flow supported by active ventilation, not by a passive diffusion. These results demonstrated that the periodic emissions of CO(2) and the associated homeostatic regulation of the respiratory acidaemia were under perfect physiological control. The termites could thus actively select the type of CO(2) release best suited to the extant environmental or internal physiological conditions, i.e. from a completely continuous respiration to occasionally cyclic or completely discontinuous CO(2) release.     

L3 and adult Ostertagia (Teladorsagia) circumcincta exhibit cyanide sensitive oxygen uptake

Oxygen consumption by L3 and adult Ostertagia (Teladorsagia) circumcincta was examined in vitro to determine whether oxygen can be utilised in metabolism. The oxygen concentration in the abomasal fluid of sheep infected with O. circumcincta was also measured. Rates of consumption (in nmol O2/h/1000 worms) were 13+/-1 in sheathed L3, 34+/-6 in ex-sheathed L3, and 1944+/-495 in adult worms. Constant rates of consumption were maintained until media oxygen concentration dropped to between 10 and 20 microM. Consumption was inhibited 95% by cyanide in L3 and 74% in adults. Oxygen concentration in abomasal fluid varied between 10 and 30 microM in both infected and uninfected animals. During infection, oxygen concentration decreased slightly with increased abomasal pH, though the correlation between the two was poor (r=-0.30). In conclusion, O. circumcincta can consume oxygen and oxygen concentration at the infection site is sufficient to support at least some aerobic metabolism.     

Studies on the extra- and intracellular acid-base status and its role on metabolic depression in the land snail <Emphasis Type="Italic">Helix lucorum</Emphasis> (L.) during estivation

The aim of the present study was to examine the acid-base status of extra- and intracellular fluids and its possible role on the regulation of the metabolic rate of Helix lucorum during prolonged estivation. For this purpose, the rate of oxygen consumption for active and estivating snails was determined. The acid-base status was also examined in the hemolymph and tissues from active and estivating snails acclimated at 25 degrees C. In addition, the buffer values of hemolymph and tissues were determined in order to examine whether there is a change in the snails during estivation. The rate of oxygen consumption decreased significantly within the 1st 10 days of estivation from 122.51+/-10 microl.g(-1).h(-1) to 25.86+/-5.2 microl.g(-1).h(-1), indicating a marked decrease in metabolic rate. P(CO2)increased within the 1st 20 days of estivation from 13.52+/-0.68 mmHg to 25.09+/-2.05 mmHg, while the pH of hemolymph (pH(e)) decreased from 7.72+/-0.04 to 7.44+/-0.06. The level of bicarbonates decreased in the hemolymph of estivating snails, indicating a metabolic acidosis, which was moderate in extracellular fluids. In contrast to pH(e), the intracellular pH (pH(i)) was maintained in the tissues of estivating H. lucorum, indicating a regulation of pH(i) despite the developed hypercapnia. According to the results presented here, it seems that the timing of pH(e) changes does not correlate with the timing of metabolic rate reduction in estivating H. lucorum.     

Water balance of over-wintering beetles in relation to strategies for cold tolerance

The vapour pressure of the haemolymph of a supercooled insect is higher than the vapour pressure of the haemolymph of a frozen insect at the same temperature. The aim of the study was to see whether this may affect the water loss of freeze-avoiding and freezetolerant, over-wintering beetles. The rates of water loss were determined on freeze-tolerant Pytho depressus larvae and Upis ceramboides adults. Within each species one group was kept supercooled whereas another group was frozen. All groups were incubated at-5°C. Both species displayed significantly lower rates of water loss when they were frozen than when they were supercooled. Values of respiratory rate and water loss of freeze-avoiding and freeze-tolerant species were compared to corresponding values of desert beetles. The results indicate that the freeze-avoiding species have lower rates of cuticular water loss than freeze-tolerant species. This indicates that the freeze-avoiding species have developed more efficient water-saving mechanisms than freeze-tolerant species. The reason for this may be that the haemolymph in frozen animals will be in vapour pressure equlibrium with the ice in the hibernaculum and thus there is no danger of desiccation during winter. The supercooled insects will have a vapour pressure of the haemolymph that is higher than the vapour pressure of water in the surrounding air and will thus lose water.Abbreviations BW body weight - BW_i initial body weight - BW_t body weight at time t - P vapour pressure difference between the water in the haemolymph and the water in the air - DWL_t dry weight loss at time t - M _w rate of metabolic water production - MF_w mol fraction of water, in the haemolymph - MO₂ rate of oxygen consumption - Osm osmolality of the haemolymph - P _a vapour pressure of water in the air - P _h vapour pressure of water in the haemolymph - P _w vapour pressure of pure water - Q a constant (2,02 1 oxygen per g fat metabolized) relating oxygen consumption to dry weight loss when fat is metabolized - R a constant (1,89 1 oxygen per g water produced) relating metabolic water production to oxygen consumption when fat is metabolized - R _dwl rate of dry weight loss - RH relative humidity of the air - RWC_i initial relative water content measured by weighing - RWC_t relative water content at time t - STP standard temperature and pressure     

Metabolic transition step from ethanol consumption to sugar/ethanol

The metabolic pathway shift between only ethanol consumption to both sugar/ethanol consumption was measured by on-line analysis of respiratory quotient of a Saccharomyces cerevisiae. The experiments were carried out in a fed-batch culture under aerobic conditions. During the transition phase, respiratory quotient (RQ) profile shows that sugar can be metabolized through the fermentative pathway even to values of RQ lower than 1.     

Metabolic and energetic control of Pseudomonas mendocina growth during transitions from aerobic to oxygen-limited conditions in chemostat cultures.

Several metabolic fluxes were analyzed during gradual transitions from aerobic to oxygen-limited conditions in chemostat cultures of Pseudomonas mendocina growing in synthetic medium at a dilution rate of 0.25 h-1. P. mendocina growth was glucose limited at high oxygen partial pressures (70 and 20% pO2) and exhibited an oxidative type of metabolism characterized by respiratory quotient (RQ) values of 1.0. A similar RQ value was obtained at low pO2 (2%), and detectable levels of acetic, formic, and lactic acids were determined in the extracellular medium. RQs of 0.9 +/- 0.12 were found at 70% pO2 for growth rates ranging from 0.025 to 0.5 h-1. At high pO2, the control coefficients of oxygen on catabolic fluxes were 0.19 and 0.22 for O2 uptake and CO2 production, respectively. At low pO2 (2%), the catabolic and anabolic fluxes were highly controlled by oxygen. P. mendocina showed a mixed-type fermentative metabolism when nitrogen was flushed into chemostat cultures. Ethanol and acetic, lactic, and formic acids were excreted and represented 7.5% of the total carbon recovered. Approximately 50% of the carbon was found as uronic acids in the extracellular medium. Physiological studies were performed under microaerophilic conditions (nitrogen flushing) in continuous cultures for a wide range of growth rates (0.03 to 0.5 h-1). A cell population, able to exhibit a near-maximum theoretical yield of ATP (YmaxATP = 25 g/mol) with a number of ATP molecules formed during the transfer of an electron towards oxygen along the respiration chain (P/O ratio) of 3, appears to have adapted to microaerophilic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolic and energetic control of Pseudomonas mendocina growth during transitions from aerobic to oxygen-limited conditions in chemostat cultures.

Several metabolic fluxes were analyzed during gradual transitions from aerobic to oxygen-limited conditions in chemostat cultures of Pseudomonas mendocina growing in synthetic medium at a dilution rate of 0.25 h-1. P. mendocina growth was glucose limited at high oxygen partial pressures (70 and 20% pO2) and exhibited an oxidative type of metabolism characterized by respiratory quotient (RQ) values of 1.0. A similar RQ value was obtained at low pO2 (2%), and detectable levels of acetic, formic, and lactic acids were determined in the extracellular medium. RQs of 0.9 +/- 0.12 were found at 70% pO2 for growth rates ranging from 0.025 to 0.5 h-1. At high pO2, the control coefficients of oxygen on catabolic fluxes were 0.19 and 0.22 for O2 uptake and CO2 production, respectively. At low pO2 (2%), the catabolic and anabolic fluxes were highly controlled by oxygen. P. mendocina showed a mixed-type fermentative metabolism when nitrogen was flushed into chemostat cultures. Ethanol and acetic, lactic, and formic acids were excreted and represented 7.5% of the total carbon recovered. Approximately 50% of the carbon was found as uronic acids in the extracellular medium. Physiological studies were performed under microaerophilic conditions (nitrogen flushing) in continuous cultures for a wide range of growth rates (0.03 to 0.5 h-1). A cell population, able to exhibit a near-maximum theoretical yield of ATP (YmaxATP = 25 g/mol) with a number of ATP molecules formed during the transfer of an electron towards oxygen along the respiration chain (P/O ratio) of 3, appears to have adapted to microaerophilic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Freezing tolerance of the European water frogs: the good, the bad, and the ugly

Survival and some physiological responses to freezing were investigated in three European water frogs (Rana lessonae, Rana ridibunda, and their hybridogen Rana esculenta). The three species exhibited different survival times during freezing (from 10 h for R. lessonae to 20 h for R. ridibunda). The time courses of percent water frozen were similar; however, because of the huge differences in body mass among species (from 10 g for Rana lessonae to nearly 100 g for Rana ridibunda), the ice mass accumulation rate varied markedly (from 0.75 +/- 0.12 to 1.43 +/- 0.11 g ice/h, respectively) and was lowest in the terrestrial hibernator Rana lessonae. The hybrid Rana esculenta exhibited an intermediate response between the two parental species; furthermore, within-species correlation existed between body mass and ice mass accumulation rates, suggesting the occurrence of subpopulations in this species (0.84 +/- 0.08 g ice/h for small R. esculenta and 1.78 +/- 0.09 g ice/h for large ones). Biochemical analyses showed accumulation of blood glucose and lactate, liver glucose (originating from glycogen), and liver alanine in Rana lessonae and Rana esculenta but not in Rana ridibunda in response to freezing. The variation of freeze tolerance between these three closely related species could bring understanding to the physiological processes involved in the evolution of freeze tolerance in vertebrates.     

Metabolic transition step from ethanol consumption to sugar/ethanol

The metabolic pathway shift between only ethanol consumption to both sugar/ethanol consumption was measured by on-line analysis of respiratory quotient of a Saccharomyces cerevisiae. The experiments were carried out in a fed-batch culture under aerobic conditions. During the transition phase, respiratory quotient (RQ) profile shows that sugar can be metabolized through the fermentative pathway even to values of RQ lower than 1.Revisions requested; Revisions received 9 September 2004     

Infradian cycles of oxygen consumption in diapausing pupae of the flesh fly, Sarcophaga crassipalpis, monitored by a scanning microrespirographic method.

Fine details of the infradian O2 consumption cycles that characterize pupal diapause in flesh flies have been monitored by a newly designed microrespirographic method coupled with an electronically regulated O2 generator. During the 4-5 days between the peaks of elevated O2 consumption, the diapausing pupae maintained a very low and fairly constant respiratory rate (13 microl O2 x g-1.h-1). During the intercalated peaks of increased respiratory metabolism, which lasted an average of 33.6 h to 24-27 degrees C, the average maximum rate of O2 consumption was 86.9 microl.g-1.h-1, a value of 6.7 times higher than the interpeak values. The respiratory peaks started abruptly in some cases while the decline was consistently gradual. During the periods between the peaks there were no discontinuous bursts of CO2 release, a feature common to diapause in many other insects. Diapause was characteristically terminated during a peak of the O2 consumption cycle. At diapause termination O2 consumption remained at the maximum values of the peak for many hours and then gradually increased to levels characteristic of nondiapause development.     

Resting metabolic rate, critical swimming speed, and routine activity of the euryhaline cyprinodontid, Aphanius dispar, acclimated to a wide range of salinities

Specimens of the euryhaline cyprinodontid fish, Aphanius dispar, collected in salt ponds, were acclimated to salinities of <1 (freshwater), 35 (seawater), 70, 105, and 140 ppt for 4 wk before measurement of oxygen consumption, critical swimming speed, and routine activity level. Oxygen consumption was similar in <1, 35, and 70 ppt (0.18+/-0.07, 0.17+/-0.06, and 0.16+/-0.04 mL h(-1) g(-1), respectively [mean+/-SD]) but decreased in 105 and 140 ppt (0. 12+/-0.02 and 0.09+/-0.2 mL h(-1) g(-1), respectively). Critical swimming speed and routine activity levels showed the same trend. These results suggest a general decrease in physiological function of A. dispar at extreme salinities.     

Walking performance and aerobic and anaerobic metabolism of Carcinus maenas (L.) in sea water at 15°C

Walking performance of the shore crab Carcinus maenas (L.) in sea water at 15 °C was assessed. In large crabs there was an inverse relationship between fatigue time and speed; crabs ran for $\text{\$}\text{?}$10 min at 3.2 m·min^?1 and for only 2 min at 14 m·min^?1. There were linear relationships between oxygen consumption and walking speeds for small and large animals walking at up to 4 m·min^?1 Estimates of maximum oxygen consumption were proportional to W^0.13 whereas inactive consumption is proportional to W^0.44 this resulted in aerobic scope (i.e. the difference between inactive and maximal rates of oxygen consumption) remaining almost constant across a weight range of animals whereas the aerobic expansibility (maximal rates/inactive rates) declined from 7- to 4-fold with increasing size. After a 12-h period without handling (settled animals) the animals could immediately become active and reach maximal rates of oxygen consumption similar to those of animals handled 1 h before the experiment. The aerobic expansibility of these settled animals could range from 21 to 8 times their inactive rates of oxygen consumption in small and large animals respectively. After 10 min of exercise oxygen consumption and whole body lactate levels returned to pre-exercise values within 5 to 25 min. The net oxygen debts range from 16 to 64% of the net oxygen consumption increase during exercise in small and large animals respectively.Calculations of the energy gained from lactate accumulation indicated that the net aerobic energy production during walking was supplemented from 4 to 71 % by anaerobic metabolism in small and large animals respectively. With increasing animal size the decline in aerobic expansibility was offset by an increased capacity for lactate production so that the overall maximum energy production during sustained activity remained almost constant at around seven times the inactive rate. The cost of transport (the net increase in oxygen consumption per g per m) falls with increased walking speed and increased animal size.     

Respiratory consequences of feeding in the snake Python molorus

Snakes can ingest large meals and exhibit marked increases in metabolic rate during digestion. Because postprandial oxygen consumption in some snakes may surpass that attained during exercise, studies of digestion offers an alternative avenue to understand the cardio-respiratory responses to elevated metabolic rate in reptiles. The effects of feeding on metabolic rate, arterial oxygen levels, and arterial acid-base status in the snake Python molorus are described. Four snakes (180-250 g) were cannulated in the dorsal aorta and blood samples were obtained during 72 h following ingestion of a meal (rat pups) exceeding 20% of body weight. Oxygen consumption increased from a fasting value of 1.71 +/- 0.08 to 5.54 +/- 0.42 ml kg-1 min-1 at 48 h following feeding, and the respiratory gas exchange ratio increased from 0.67 +/- 0.02 to a maximum of 0.92 +/- 0.03 at 32 h. Plasma lactate was always less than 0.5 mM, so the postprandial increase in metabolic rate was met by aerobic respiration. In fasting animals, arterial PO2 was 66 +/- 4 mmHg and haemoglobin-O2 saturation was 92 +/- 3%; similar values were recorded during digestion, but haematocrit decreased from 15.8 +/- 1.0 to 9.8 +/- 0.8 due to repeated blood sampling. Plasma [HCO3-] increased from a fasting level of 19.3 +/- 0.8 to 25.8 +/- 1.0 mmol l-1 at 24 h after feeding. However, because arterial PCO2 increased from 21.1 +/- 0.5 to 27.9 +/- 1.4 mmHg, there was no significant change in arterial pH from the fasting value of 7.52 +/- 0.01. Acid-base status returned to pre-feeding levels at 72 h following feeding. The increased arterial PCO2 is most likely explained by a reduction in ventilation relative to metabolism, but we predict that lung PO2 does not decrease below 115 mmHg. Although ingestion of large meals is associated with large metabolic changes in pythons, the attendant changes in blood gases are relatively small. In particular, the small changes in plasma [HCO3-] and stable pH show that pythons respond very differently to digestion than alligators where very large alkaline tides have been observed. It is unclear why pythons and alligators differ in the magnitude of their responses, but given these interspecific differences it seems worthwhile to describe arterial blood gases during digestion in other species of ectothermic vertebrates.     

The effect of seasonality on oxidative metabolism in Nacella (Patinigera) magellanica

We studied the seasonal variation on aerobic metabolism and the response of oxidative stress parameters in the digestive glands of the subpolar limpet Nacella (P.) magellanica. Sampling was carried out from July (winter) 2002 to July 2003 in Beagle Channel, Tierra del Fuego, Argentina. Whole animal respiration rates increased in early spring as the animals spawned and remained elevated throughout summer and fall (winter: 0.09+/-0.02 micromol O2 h-1 g-1; summer: 0.31+/-0.06 micromol O2 h-1 g-1). Oxidative stress was assessed at the hydrophilic level as the ascorbyl radical content/ascorbate content ratio (A./AH-). The A./AH- ratio showed minimum values in winter (3.7+/-0.2 10(-5)AU) and increased in summer (18+/-5 10(-5) AU). A similar pattern was observed for lipid radical content (122+/-29 pmol mg-1 fresh mass [FW] in winter and 314+/-45 pmol mg-1 FW in summer), iron content (0.99+/-0.07 and 2.7+/-0.6 nmol mg-1 FW in winter and summer, respectively) and catalase activity (2.9+/-0.2 and 7+/-1 U mg-1 FW in winter and summer, respectively). Since nitrogen derived radicals are thought to be critically involved in oxidative metabolism in cells, nitric oxide content was measured and a significant difference in the content of the Fe-MGD-NO adduct in digestive glands from winter and summer animals was observed. Together, the data indicate that both oxygen and nitrogen radical generation rates in N. (P.) magellanica are strongly dependent on season.     

Effects of loaded breathing and hypoxia on diaphragm metabolism as measured by (31)P-NMR spectroscopy.

Diaphragm fatigue may contribute to respiratory failure. (31)P-nuclear magnetic resonance spectroscopy is a useful tool to assess energetic changes within the diaphragm during fatigue, as indicated by P(i) accumulation and phosphocreatine (PCr) depletion. We hypothesized that loaded breathing during hypoxia would lead to diaphragm fatigue and inadequate aerobic metabolism. Seven piglets were anesthetized by using halothane inhalation. Diaphragmatic contractility was assessed by transdiaphragmatic pressure (Pdi) at end expiration with the airway occluded. A nuclear magnetic resonance surface coil placed under the right hemidiaphragm measured P(i) and PCr during four conditions: control, inspiratory resistive breathing (IRB), IRB with hypoxia, and recovery (IRB without hypoxia). IRB alone resulted in hypercarbia (32 +/- 7 to 61 +/- 21 Torr) and respiratory acidosis but no change in diaphragm force output or aerobic metabolism. Combined IRB and hypoxia resulted in decreased force output (Pdi decreased by 40%; from 30 +/- 17 to 19 +/- 11 mmHg) and evidence of metabolic stress (ratio of P(i) to PCr increased by 290%; from 0.19 +/- 0.09 to 0.74 +/- 0.27). We conclude that diaphragm fatigue associated with inadequate aerobic oxidative metabolism occurs in the setting of loaded breathing and hypoxia. Conversely, aerobic metabolism and force output of the diaphragm remain unchanged from control during loaded normoxic or hyperoxic breathing despite the onset of respiratory failure.     

Morphometric analysis of the larval branchial chamber in the dragonfly Aeshna cyanea Müller (Insecta, Odonata, Anisoptera)

The aquatic larvae of anisopteran dragonflies possess tracheal gills located in the rectum. Using stereological methods, we estimated the morphometric diffusing capacity for oxygen (D(MO2)) across the gill epithelium, i.e., from rectal water to the gill tracheoles, in the larvae of Aeshna cyanea. A 271-mg larva has a total branchial surface area of approximately 12 cm(2). Tracheoles make up 6% of the epithelial volume of the gills; the harmonic mean thickness of the water-tracheolar diffusion barrier is 0.27 microm and consists mainly of cuticle. The calculated D(MO2) is 23.0 microl min(-1) g(-1) kPa(-1), which, using published values for oxygen consumption in a similar species, would result in a mean driving pressure of 0.2 kPa at rest and 1.3 kPa during activity. Since these driving pressures are similar to those reported for other arthropods, we conclude that the D(MO2) of the gill is not rate-limiting for aerobic metabolism in Aeshna cyanea larvae. J Morphol. 261:81-91, 2004.     

Energy metabolism of cultured TM4 cells and the action of gossypol

The energy metabolism of cultured TM4 cells, a cell line originally derived from mouse testicular cells, has been studied in relation to the action of gossypol. In the absence of externally added substrates, TM4 cells consumed oxygen at 37 +/- 5 nmoles O2 X mg protein-1 X h-1. Pyruvate stimulated oxygen consumption in a dose-dependent fashion up to 23%. Addition of glucose to the cells suspended in substrate-free medium inhibited oxygen consumption. At 5.5 mM glucose, the inhibition of oxygen consumption was 45 +/- 9%. The rate of aerobic lactate production from endogenous substrates was less than 7 nmoles lactate X mg protein-1 X h-1, even in the presence of optimal concentrations of the mitochondrial uncoupler carbonylcyanide m-chlorophenylhydrazone. The rate of aerobic lactate production was 920 +/- 197 nmoles X mg protein-1 X h-1 at external glucose concentrations of 2 mM or greater. The formation of aerobic glycolytic adenosine triphosphate (ATP) in 5 mM glucose comprised about 80% of the total ATP production. Gossypol stimulated both aerobic lactate production and oxygen consumption of the transformed testicular cells in a dose-dependent manner. The effect of gossypol on glucose transport, aerobic lactate production, and oxygen consumption is consistent with the hypothesis that gossypol modifies energy metabolism in these cells mainly by partially uncoupling mitochondrial oxidative phosphorylation. The possible impairment of cell and tissue function under gossypol treatment would depend on the metabolic properties of each specific differentiated cell.     

Physiology and biochemistry of the pseudobranch: an unanswered question?

The structure and function of the pseudobranch has long interested scientists, but its overall role has remained a mystery. Previous studies have attributed respiratory, endocrine, osmoregulatory and sensory roles to the pseudobranch, and the present review concentrates on new findings. Perfusion experiments on the pseudobranch of the rainbow trout (Oncorhynchus mykiss) using both erythrocyte suspensions and Ringer solution have shown that this organ is able to generate values for the respiratory quotient (RQ) greater than 1.0. The release of carbon dioxide into the perfusate was found to be largely independent of flow between perfusion rates of 120-190 microl/min and could be inhibited by acetazolamide (10(-5) M), indicating a role for carbonic anhydrase. Noradrenaline (10(-5) M) had no effect on oxygen consumption or carbon dioxide release of the pseudobranch. The rate of carbon dioxide release was also dependent on the pH of the pre-pseudobranch perfusate, carbon dioxide release being reduced at lower perfusate pH values. Based on the glucose balance of the isolated saline-perfused rainbow trout pseudobranch and on the enzyme profiles for the rainbow trout, cod, swordfish and deep-water grenadier pseudobranch, it is suggested that the pentose phosphate shunt might be a source of carbon dioxide, yielding the high RQ values found for this organ. Most evidence now available indicates that the pseudobranch is integrally linked with the choroid rete and the supply of oxygen to the retina of the fish eye.     

Aerial and aquatic respiration of the Australian desert goby, Chlamydogobius eremius

Physiological, anatomical and behavioural adaptations enable the Australian desert goby, Chlamydogobius eremius, to live in mound springs and temporary aquatic habitats surrounding the south-eastern rim of the Lake Eyre drainage basin in the harsh inland of Australia. This study describes the desert goby's respiratory and metabolic responses to hypoxic conditions and its use of buccal air bubbles for gas exchange at the water surface. Oxygen consumption for C. eremius is significantly higher in water than in air under normoxic and hypoxic conditions. In water, total oxygen consumption (V(O(2))) increases from normoxic conditions (253 microl g(-1) h(-1)) to 8% ambient O(2) concentration (377 microl g(-1) h(-1)), then decreases with increasing hypoxia of 4% O(2) (226 microl g(-1) h(-1)) and at 2% O(2) (123 microl g(-1) h(-1)). In air (fish were moist but out of water), V(O(2)) progressively decreases from normoxic conditions to hypoxic conditions (21% O(2), V(O(2)) is 169 microl g(-1) h(-1) to 39 microl g(-1) h(-1) at 2% O(2)). These data indicate oxygen-conforming patterns with increasing hypoxia both in air and in water below 8% O(2). In water, opercular movement rates remain unchanged with increasing hypoxia (139 min(-1) at 21% O(2), 154 min(-1) at 8%, 156 min(-1) at 4% and 167 min(-1) at 2%) but in air, opercular movement rates are significantly lower than in water, corresponding with the lower metabolic rate (71 min(-1) at 21% O(2), 53 min(-1) at 8%, 96 min(-1) at 4% and 64 min(-1) at 2%). Chlamydogobius eremius can use a buccal air bubble for aerial O(2) uptake, most probably in response to increased aquatic hypoxia. In air, C. eremius relies more on the buccal bubble as an oxygen source with increasing hypoxia up to an ambient O(2) of 4% (7.1% of V(O(2)) at 21% O(2); 14.5% at 8% O(2); and 27.1% at 4% O(2)), then when the available supply of O(2) is further reduced, it decreases (15% of V(O(2)) at 2% O(2)) and respiration across the skin again makes a higher relative contribution. The Australian desert goby has a higher metabolic rate in higher salinities (336 microl g(-1) h(-1) in 35 ppt, 426 microl g(-1) h(-1) in 70 ppt) than in freshwater (235 microl O(2) g(-1) h(-1)), presumably because of the increased metabolic cost of osmoregulation. There was no significant difference in V(O(2)) for fish in air that had come from varying salinities.